perf: retain mount state across mixed geometry and paint updates

ebox-surface.el

@@ -1805,6 +1805,13 @@ the projection roots a second time."
               (ebox-surface--native-full-frame-p state projection-kind)))
          (previous-owned-ranges
           (plist-get state :previous-surface-owned-ranges))
+         (retained-owned-ranges
+          (and (eq projection-kind 'mixed-owner-reflow)
+               (eq (plist-get (plist-get state :mixed-owner-proof)
+                              :geometry-kind)
+                   'span-patch)
+               (not (ebox-surface--mixed-range-splice-p state))
+               (plist-get state :span-patch-retained-owned-ranges)))
          (node-objects
           (or (and scroll-fast-p
                    (plist-get state :surface-node-object-table))
@@ -1818,6 +1825,7 @@ the projection roots a second time."
     ;; Paint contributions belong to this one publication.  Keep them out of
     ;; the transferred client state so later paint cannot replay old layers.
     (cl-remf state :paint-property-contributions)
+    (cl-remf state :span-patch-retained-owned-ranges)
     (plist-put state :surface-node-object-table node-objects)
     (plist-put state :region-surface-object-table region-objects)
     (unless (and scroll-fast-p
@@ -1831,11 +1839,12 @@ the projection roots a second time."
     (or (and native-retained-p
              (ebox-surface--native-patch-result
               context projection state output node-objects region-objects))
-        (and (null property-contributions)
+        (and (or (null property-contributions) retained-owned-ranges)
              (memq projection-kind
                    '(span-patch owner-scoped mixed-owner-reflow))
              (ebox-surface--span-coordinate-result
-              context projection state output previous-owned-ranges))
+              context projection state output previous-owned-ranges
+              property-contributions retained-owned-ranges))
         (let* ((range-splice-p
                 (and (eq projection-kind 'mixed-owner-reflow)
                      (ebox-surface--mixed-range-splice-p state)))
@@ -1849,9 +1858,15 @@ the projection roots a second time."
           (or (and (null property-contributions)
                    (memq projection-kind
                           '(span-patch owner-scoped mixed-owner-reflow))
-                   (ebox-surface--coordinate-commit
+                   (when-let* ((batch
-                    context state rendered owned-ranges (nth 3 prepared)
+                                (ebox-surface--coordinate-batch
-                    previous-owned-ranges))
+                                 state rendered previous-owned-ranges)))
+                     (tp-commit-batch-result-create
+                      context batch
+                      :mount-specs
+                      (ebox-surface--commit-mount-specs
+                       (nth 3 prepared) owned-ranges)
+                      :client-state state)))
               (if (and (not range-splice-p)
                        (or full-surface-p native-retained-p
                            property-contributions))
@@ -1965,13 +1980,68 @@ content projection order; fragment and surface records follow unchanged."
            (ebox-surface--commit-mount-specs mount-records owned-ranges)
            :client-state state))))))
 
-(defun ebox-surface--coordinate-commit
+(defun ebox-surface--patch-property-contributions
-    (context state rendered owned-ranges mount-records previous-owned-ranges)
+    (patches contributions extent)
-  "Return STATE's exact proven-owner coordinate commit, or nil.
+  "Return fresh PATCHES carrying completely covered CONTRIBUTIONS, or nil.
-PREVIOUS-OWNED-RANGES identify the committed owner intervals.  The mixed
+CONTRIBUTIONS use target coordinates bounded by EXTENT.  Preserve their order
+inside every patch; a gap rejects the batch rather than dropping paint."
+  (when (proper-list-p contributions)
+    (catch 'uncovered
+      (let* ((targets (vconcat (mapcar #'copy-sequence patches)))
+             (count (length targets))
+             (layers (make-vector count nil)))
+        (dolist (contribution contributions)
+          (let ((start (plist-get contribution :start))
+                (end (plist-get contribution :end))
+                (props (plist-get contribution :props)))
+            ;; Validate the original interval before clipping.  On a proof
+            ;; miss the retained-content path reports invalid inputs through
+            ;; TP's ordinary contribution validator.
+            (unless (and (integerp start) (integerp end)
+                         (<= 0 start end extent)
+                         (ebox-style--valid-plist-p props)
+                         (cl-loop for (key _value) on props by #'cddr
+                                  always (symbolp key)))
+              (throw 'uncovered nil))
+            (when (< start end)
+              (let ((low 0) (high count) (position start))
+                ;; Patches are ordered and disjoint.  Locate the first one
+                ;; once per layer, then visit only its actual intersections.
+                (while (< low high)
+                  (let ((middle (/ (+ low high) 2)))
+                    (if (<= (plist-get (aref targets middle) :new-end) start)
+                        (setq low (1+ middle))
+                      (setq high middle))))
+                (while (< position end)
+                  (when (>= low count) (throw 'uncovered nil))
+                  (let* ((patch (aref targets low))
+                         (patch-start (plist-get patch :new-start))
+                         (next (min end (plist-get patch :new-end))))
+                    (when (> patch-start position) (throw 'uncovered nil))
+                    (when (< position next)
+                      (push (list :start (- position patch-start)
+                                  :end (- next patch-start) :props props)
+                            (aref layers low)))
+                    (setq position next low (1+ low))))))))
+        (dotimes (index count)
+          (when (aref layers index)
+            (aset targets index
+                  (plist-put (aref targets index) :property-contributions
+                             (nreverse (aref layers index))))))
+        (append targets nil)))))
+
+(defun ebox-surface--coordinate-batch
+    (state rendered previous-owned-ranges
+           &optional property-contributions retained-origin)
+  "Return STATE's exact proven-owner coordinate batch, or nil.
+RENDERED is the candidate text.  PREVIOUS-OWNED-RANGES identify the committed
+owner intervals.  The mixed
 projection has already produced exact coordinate patches and final text; this
 function composes those retained facts into TP's standard validated commit
-batch without asking TP to rediscover the same diff from a full plan."
+batch without asking TP to rediscover the same diff from a full plan.
+PROPERTY-CONTRIBUTIONS add ordered target paint.  RETAINED-ORIGIN is the live
+surface origin when an exact ownership proof permits indexed owner lookup.
+This proof step does not register objects in the active prepare context."
   (let* ((proof (plist-get state :mixed-owner-proof))
          (owner-ids
           (or (plist-get proof :owner-ids)
@@ -2006,19 +2076,32 @@ batch without asking TP to rediscover the same diff from a full plan."
                      :new-start (plist-get patch :new-start)
                      :new-end (plist-get patch :new-end)))
              coordinate-patches))
-      (dolist (range previous-owned-ranges)
+      (if retained-origin
-        (when (gethash (plist-get range :object) owner-set)
+          ;; The strict retained-property witness preserves the complete
-          (when-let* ((new-start
+          ;; mount projection.  Read just the changed owners from TP's
-                      (ebox-surface--rebase-coordinate
+          ;; existing index, including baseline-only paint removals.
-                       (plist-get range :start) coordinate-patches))
+          (maphash
-                     (new-end
+           (lambda (object _present)
-                      (ebox-surface--rebase-coordinate
+             (dolist (mount (tp-object-mounts object))
-                       (plist-get range :end) coordinate-patches)))
+               (let ((start (- (plist-get mount :start) retained-origin))
-            (push (list :old-start (plist-get range :start)
+                     (end (- (plist-get mount :end) retained-origin)))
-                        :old-end (plist-get range :end)
+                 (push (list :old-start start :old-end end
-                        :new-start (car new-start)
+                             :new-start start :new-end end)
-                        :new-end (car new-end))
+                       intervals))))
-                  intervals))))
+           owner-set)
+        (dolist (range previous-owned-ranges)
+          (when (gethash (plist-get range :object) owner-set)
+            (when-let* ((new-start
+                        (ebox-surface--rebase-coordinate
+                         (plist-get range :start) coordinate-patches))
+                       (new-end
+                        (ebox-surface--rebase-coordinate
+                         (plist-get range :end) coordinate-patches)))
+              (push (list :old-start (plist-get range :start)
+                          :old-end (plist-get range :end)
+                          :new-start (car new-start)
+                          :new-end (car new-end))
+                    intervals)))))
       (setq intervals
             (sort intervals
                   (lambda (left right)
@@ -2077,56 +2160,103 @@ batch without asking TP to rediscover the same diff from a full plan."
                           :patches patches
                           :coordinate-patches intervals)
                        (tp-surface-error nil)))))
+          (when (and batch property-contributions)
+            (setq batch
+                  (when-let* ((layered
+                               (ebox-surface--patch-property-contributions
+                                patches property-contributions target-extent)))
+                    ;; The bare batch above proves geometry.  Composition
+                    ;; runs outside its proof-miss catch: a merger can signal
+                    ;; any condition, including `tp-surface-error', and must
+                    ;; preserve ordinary transaction failure and rollback.
+                    (tp-commit-batch-create
+                     :base-revision base-revision
+                     :target-revision (1+ base-revision)
+                     :base-extent source-extent :target-extent target-extent
+                     :patches layered :coordinate-patches intervals))))
           (when batch
-            (prog1
+            (cl-remf state :content-base-extent)
+            batch))))))
+
+(defun ebox-surface--span-coordinate-result
+    (context projection state rendered previous-owned-ranges
+             &optional property-contributions retained-owned-ranges)
+  "Return a direct span commit from retained coordinate metadata, or nil.
+CONTEXT and PROJECTION supply retained object identities.  STATE and RENDERED
+hold the candidate coordinates and text; PREVIOUS-OWNED-RANGES is the committed
+ownership snapshot.  PROPERTY-CONTRIBUTIONS are ordered candidate paint layers.
+RETAINED-OWNED-RANGES witnesses unchanged ownership when it is that snapshot."
+  (let* ((patches (plist-get state :content-coordinate-patches))
+         (surface-root (plist-get projection :surface-root))
+         (retained-origin
+          (when (and surface-root patches retained-owned-ranges
+                     (eq retained-owned-ranges previous-owned-ranges)
+                     (equal (plist-get state :content-base-extent)
+                            (length rendered))
+                     (cl-every
+                      (lambda (patch)
+                        (and (= (plist-get patch :old-start)
+                                (plist-get patch :new-start))
+                             (= (plist-get patch :old-end)
+                                (plist-get patch :new-end))))
+                      patches))
+            (let ((mounts (tp-object-mounts surface-root)))
+              (when (and (= (length mounts) 1)
+                         (= (- (plist-get (car mounts) :end)
+                               (plist-get (car mounts) :start))
+                            (length rendered)))
+                (plist-get (car mounts) :start))))))
+    (when-let* ((fragments
+                 (and surface-root patches
+                      (or (plist-get state :mixed-owner-fragment-data)
+                          (plist-get state :span-patch-fragment-data))))
+                (rebased
+                 (if retained-origin
+                     (cons t previous-owned-ranges)
+                   (and (null property-contributions) previous-owned-ranges
+                        (ebox-surface--rebase-owned-ranges
+                         previous-owned-ranges patches (length rendered)))))
+                (batch
+                 (ebox-surface--coordinate-batch
+                  state rendered previous-owned-ranges
+                  property-contributions retained-origin))
+                (fragment-root
+                 (tp-object-ensure context surface-root
+                                   ebox-surface--fragments-key 'ebox/fragments))
+                (text-leaf
+                 (tp-object-ensure context fragment-root
+                                   ebox-surface--text-key 'ebox/text)))
+      (let* ((owned-ranges (cdr rebased))
+             (rendered-length (length rendered))
+             (mount-records
+              (unless retained-origin
+                (list (list :object text-leaf :start 0 :end rendered-length
+                            :props nil :tags nil :leaf t)
+                      (list :object fragment-root :start 0 :end rendered-length
+                            :props nil :tags nil :leaf nil)
+                      (list :object surface-root :start 0 :end rendered-length
+                            :props nil :tags nil :leaf nil))))
+             (result
+              (if retained-origin
+                  (tp-commit-batch-result-create
+                   context batch :client-state state :reuse-mount-projection t)
                 (tp-commit-batch-result-create
                  context batch
                  :mount-specs
                  (ebox-surface--commit-mount-specs mount-records owned-ranges)
-                 :client-state state)
+                 :client-state state))))
-              (cl-remf state :content-base-extent))))))))
+        (when result
-
+          (plist-put state :surface-owned-ranges
-(defun ebox-surface--span-coordinate-result
+                     (if retained-origin
-    (context projection state rendered previous-owned-ranges)
+                         owned-ranges
-  "Return a direct span commit from retained coordinate metadata, or nil."
+                       (ebox-surface--snapshot-owned-ranges owned-ranges)))
-  (when-let* ((fragments
+          (plist-put state :surface-fragments fragments)
-               (or (plist-get state :mixed-owner-fragment-data)
+          (cl-remf state :previous-surface-owned-ranges)
-                   (plist-get state :span-patch-fragment-data)))
+          (cl-remf state :mixed-owner-fragment-data)
-              (patches (plist-get state :content-coordinate-patches))
+          (cl-remf state :mixed-owner-content-p)
-              (rebased
+          (cl-remf state :span-patch-fragment-data)
-               (and previous-owned-ranges
+          (cl-remf state :span-patch-content-p)
-                    (ebox-surface--rebase-owned-ranges
+          result)))))
-                     previous-owned-ranges patches (length rendered))))
-              (surface-root (plist-get projection :surface-root))
-              (fragment-root
-               (tp-object-ensure context surface-root
-                                 ebox-surface--fragments-key 'ebox/fragments))
-              (text-leaf
-               (tp-object-ensure context fragment-root
-                                 ebox-surface--text-key 'ebox/text)))
-    (let* ((owned-ranges (cdr rebased))
-           (rendered-length (length rendered))
-           (mount-records
-            (list (list :object text-leaf :start 0 :end rendered-length
-                        :props nil :tags nil :leaf t)
-                  (list :object fragment-root :start 0 :end rendered-length
-                        :props nil :tags nil :leaf nil)
-                  (list :object surface-root :start 0 :end rendered-length
-                        :props nil :tags nil :leaf nil)))
-           (result
-            (ebox-surface--coordinate-commit
-             context state rendered owned-ranges mount-records
-             previous-owned-ranges)))
-      (when result
-        (plist-put state :surface-owned-ranges
-                   (ebox-surface--snapshot-owned-ranges owned-ranges))
-        (plist-put state :surface-fragments fragments)
-        (cl-remf state :previous-surface-owned-ranges)
-        (cl-remf state :mixed-owner-fragment-data)
-        (cl-remf state :mixed-owner-content-p)
-        (cl-remf state :span-patch-fragment-data)
-        (cl-remf state :span-patch-content-p)
-        result))))
 
 (defun ebox-surface--mounted-object-for-node (state node-id)
   "Return NODE-ID's nearest live retained object with mounts in STATE."
@@ -3926,7 +4056,10 @@ Proof mismatches return nil; unexpected rendering errors propagate."
                               output old-fragments
                               (plist-get state :content-coordinate-patches)))))
                 (plist-put state :span-patch-fragment-data fragments)
-                (plist-put state :span-patch-content-p t))
+                (plist-put state :span-patch-content-p t)
+                (when (and retained-properties-p (not coordinate-shift-p))
+                  (plist-put state :span-patch-retained-owned-ranges
+                             (plist-get previous-state :surface-owned-ranges))))
               output)))))))
 
 (defun ebox-surface--formatting-context-reflow-lines
@@ -5617,6 +5750,7 @@ but cannot introduce or remove a viewport expression or node identity."
             (ebox--new-buffer-render-state root))
           (copy-sequence state-overrides))))
     (cl-remf state :paint-property-contributions)
+    (cl-remf state :span-patch-retained-owned-ranges)
     (plist-put state :root-node root)
     (when (plist-get state :native-sync-confirmed-p)
       (ebox-native-commit-attach-confirmed-base previous-state state))

tests/ebox-child-range-tests.el

@@ -948,6 +948,23 @@
               (ebox-child-range-test--assert-current-snapshot
                (current-buffer) ancestor))))))))
 
+(defun ebox-child-range-test--mixed-followup-candidate (buffer selected &optional title)
+  "Return BUFFER's title and row-paint candidate for SELECTED, using TITLE."
+  (let ((candidate (ebox-candidate-begin buffer)))
+    (ebox-candidate-replace-host-ref
+     candidate 'title
+     (ebox-test-text (propertize (or title (format "title-%d" selected))
+                                'face '(:weight bold))
+                     :key 'title :source-identity 'title))
+    (dolist (row '(1 2))
+      (let ((ref (intern (format "row-%d" row))))
+        (ebox-candidate-replace-host-ref
+         candidate ref
+         (ebox-test-box :key ref :source-identity ref
+           :color (if (= row selected) "#123456" "#654321")
+           (ebox-test-text (format "row-%d" row))))))
+    candidate))
+
 (ert-deftest ebox-child-range-retained-kind-replacement-allows-mixed-followups ()
   "Later title and row paint edits remain local beside disjoint scrolling."
   (with-temp-buffer
@@ -960,6 +977,12 @@
      (current-buffer)
      (ebox-child-range-test--replace-snapshot-detail (current-buffer) t))
     (let* ((state (ebox--buffer-render-state (current-buffer)))
+           (surface ebox-surface--buffer-surface)
+           (mounts (tp--surface-mounts surface))
+           (mount-ids (mapcar #'tp--surface-mount-id mounts))
+           (mount-index (tp--surface-mount-index surface))
+           (index (tp--surface-index surface))
+           (ranges (plist-get state :surface-owned-ranges))
            (scroll-id (car (plist-get state :scroll-region-ids)))
            (scroll (gethash scroll-id ebox--scroll-global-state))
            (raw (plist-get scroll :content-lines))
@@ -972,22 +995,12 @@
       (should scroll-id)
       (should (= (length (plist-get state :scroll-region-ids)) 1))
       (dolist (selected '(2 1 2))
-        (let* ((candidate (ebox-candidate-begin (current-buffer)))
+        (let* ((candidate
+                (ebox-child-range-test--mixed-followup-candidate
+                 (current-buffer) selected))
                (root-renders 0)
                (observer (lambda (&rest _arguments) (cl-incf root-renders)))
                report)
-          (ebox-candidate-replace-host-ref
-           candidate 'title
-           (ebox-test-text (propertize (format "title-%d" selected)
-                                      'face '(:weight bold))
-                           :key 'title :source-identity 'title))
-          (dolist (row '(1 2))
-            (let ((ref (intern (format "row-%d" row))))
-              (ebox-candidate-replace-host-ref
-               candidate ref
-               (ebox-test-box :key ref :source-identity ref
-                 :color (if (= row selected) "#123456" "#654321")
-                 (ebox-test-text (format "row-%d" row))))))
           (advice-add 'ebox-surface--render-candidate :before observer)
           (unwind-protect
               (setq report (ebox-commit (current-buffer) candidate))
@@ -1001,11 +1014,308 @@
                              selected root-renders report))
             (should (eq (plist-get report :projection-kind) 'mixed-owner-reflow))
             (should (zerop root-renders))
-            (should-not (plist-get report :tp-full-root)))
+            (should-not (plist-get report :tp-full-root))
+            (should (plist-get (tp-surface-report surface) :commit-batch))
+            (should (plist-get (tp-surface-report surface) :retained-mount-state))
+            (should (eq mounts (tp--surface-mounts surface)))
+            (should (equal mount-ids
+                           (mapcar #'tp--surface-mount-id
+                                   (tp--surface-mounts surface))))
+            (should (eq mount-index (tp--surface-mount-index surface)))
+            (should (eq index (tp--surface-index surface)))
+            (should (eq ranges
+                        (plist-get (ebox--buffer-render-state (current-buffer))
+                                   :surface-owned-ranges))))
           (let ((next-scroll (gethash scroll-id ebox--scroll-global-state)))
             (should (eq raw (plist-get next-scroll :content-lines)))
             (should (eq rendered (plist-get next-scroll :rendered-content-lines)))))))))
 
+(ert-deftest ebox-child-range-mixed-followup-publish-failure-restores-and-retries ()
+  "A failed public mixed commit restores the old generation before retry."
+  (with-temp-buffer
+    (ebox-render-to-buffer
+     (current-buffer) (ebox-child-range-test--snapshot-replacement-root))
+    (ebox--ensure-layout-snapshot-details
+     (current-buffer)
+     (plist-get (ebox--host-ref-node (current-buffer) 'detail) :node-id))
+    (ebox-commit
+     (current-buffer)
+     (ebox-child-range-test--replace-snapshot-detail (current-buffer) t))
+    (let* ((state (ebox--buffer-render-state (current-buffer)))
+           (surface ebox-surface--buffer-surface)
+           (revision (tp-surface-revision surface))
+           (previous-report (tp-surface-report surface))
+           (before (buffer-string))
+           (mounts (tp--surface-mounts surface))
+           (mount-ids (mapcar #'tp--surface-mount-id mounts))
+           (mount-index (tp--surface-mount-index surface))
+           (index (tp--surface-index surface))
+           (ranges (plist-get state :surface-owned-ranges))
+           (scroll-id (car (plist-get state :scroll-region-ids)))
+           (scroll (gethash scroll-id ebox--scroll-global-state))
+           trace)
+      (should-error
+       (ebox-commit
+        (current-buffer)
+        (ebox-child-range-test--mixed-followup-candidate (current-buffer) 2)
+        (lambda (_report) (push 'publish trace) (error "reject mixed publication"))
+        (lambda (_report) (push 'rollback trace))))
+      (should (equal trace '(rollback publish)))
+      (should (eq state (ebox--buffer-render-state (current-buffer))))
+      (should (eq state (tp-surface-client-state surface)))
+      (should (= revision (tp-surface-revision surface)))
+      (should (eq ranges (plist-get state :surface-owned-ranges)))
+      (should (eq mounts (tp--surface-mounts surface)))
+      (should (equal mount-ids (mapcar #'tp--surface-mount-id mounts)))
+      (should (eq mount-index (tp--surface-mount-index surface)))
+      (should (eq index (tp--surface-index surface)))
+      (should (eq scroll (gethash scroll-id ebox--scroll-global-state)))
+      (should (equal-including-properties before (buffer-string)))
+      (should (equal previous-report (tp-surface-report surface)))
+      (let ((report
+             (ebox-commit
+              (current-buffer)
+              (ebox-child-range-test--mixed-followup-candidate
+               (current-buffer) 2))))
+        (ebox-child-range-test--assert-full-render-equivalent (current-buffer))
+        (should (= (1+ revision) (tp-surface-revision surface)))
+        (should (eq (plist-get report :projection-kind) 'mixed-owner-reflow))
+        (should-not (plist-get report :tp-full-root))
+        (should (plist-get (tp-surface-report surface) :commit-batch))
+        (should (plist-get (tp-surface-report surface) :retained-mount-state))
+        (should (eq mounts (tp--surface-mounts surface)))
+        (should (equal mount-ids (mapcar #'tp--surface-mount-id mounts)))
+        (should (eq mount-index (tp--surface-mount-index surface)))
+        (should (eq index (tp--surface-index surface)))
+        (should (eq (plist-get scroll :content-lines)
+                    (plist-get (gethash scroll-id ebox--scroll-global-state)
+                               :content-lines)))))))
+
+(ert-deftest ebox-child-range-mixed-followup-removes-face-without-contribution ()
+  "A paint owner with no new face still publishes its baseline-only removal."
+  (with-temp-buffer
+    (ebox-render-to-buffer
+     (current-buffer)
+     (ebox-test-column :width '(200)
+       (ebox-test-column :bgcolor "#DDE7EF"
+         (ebox-test-text (propertize "title-1" 'face '(:weight bold))
+                         :key 'title :source-identity 'title))
+       (ebox-test-box :key 'row-1 :source-identity 'row-1 :color "#123456"
+         (ebox-test-text (propertize "row-1" 'face '(:slant italic))))))
+    (let* ((surface ebox-surface--buffer-surface)
+           (mounts (tp--surface-mounts surface))
+           (mount-index (tp--surface-mount-index surface))
+           (candidate (ebox-candidate-begin (current-buffer)))
+           (observed nil) (contributions 'not-observed)
+           (observer
+            (lambda (_context _projection state _output &optional kind)
+              (when (eq kind 'mixed-owner-reflow)
+                (setq observed t
+                      contributions (plist-get state :paint-property-contributions)))))
+           report)
+      (ebox-candidate-replace-host-ref
+       candidate 'title
+       (ebox-test-text (propertize "title-2" 'face '(:weight bold))
+                       :key 'title :source-identity 'title))
+      (ebox-candidate-replace-host-ref
+       candidate 'row-1
+       (ebox-test-box :key 'row-1 :source-identity 'row-1
+         (ebox-test-text (propertize "row-1" 'face '(:slant italic)))))
+      (advice-add 'ebox-surface--projection-result :before observer)
+      (unwind-protect
+          (setq report (ebox-commit (current-buffer) candidate))
+        (advice-remove 'ebox-surface--projection-result observer))
+      (ebox-child-range-test--assert-full-render-equivalent (current-buffer))
+      (should observed)
+      (should-not contributions)
+      (should (eq (plist-get report :projection-kind) 'mixed-owner-reflow))
+      (should (equal (get-text-property (string-match "row-1" (buffer-string))
+                                       'face (buffer-string))
+                     '(:slant italic)))
+      (should (plist-get (tp-surface-report surface) :commit-batch))
+      (should (plist-get (tp-surface-report surface) :retained-mount-state))
+      (should (eq mounts (tp--surface-mounts surface)))
+      (should (eq mount-index (tp--surface-mount-index surface))))))
+
+(ert-deftest ebox-child-range-mixed-followup-coordinate-change-keeps-fallback ()
+  "A longer title cannot claim the stable-coordinate mount-reuse proof."
+  (with-temp-buffer
+    (ebox-render-to-buffer
+     (current-buffer) (ebox-child-range-test--snapshot-replacement-root))
+    (ebox-commit
+     (current-buffer)
+     (ebox-child-range-test--replace-snapshot-detail (current-buffer) t))
+    (let ((extent (buffer-size)))
+      (ebox-commit
+       (current-buffer)
+       (ebox-child-range-test--mixed-followup-candidate
+        (current-buffer) 2 "title-2 with a longer extent"))
+      (should-not (= extent (buffer-size))))
+    (ebox-child-range-test--assert-full-render-equivalent (current-buffer))
+    (should-not (plist-get (tp-surface-report ebox-surface--buffer-surface)
+                           :retained-mount-state))))
+
+(ert-deftest ebox-child-range-mixed-followup-patch-layers-require-complete-coverage ()
+  "Ordered paint may cross adjacent patches, but cannot disappear into a gap."
+  (let* ((baseline (propertize "abcdefgh" 'face 'bold 'help-echo "base"))
+         (patches
+          (mapcar (lambda (range)
+                    (list :old-start (car range) :old-end (cdr range)
+                          :new-start (car range) :new-end (cdr range)
+                          :replacement (substring baseline (car range) (cdr range))))
+                  '((0 . 2) (2 . 4) (6 . 8))))
+         (before (copy-tree patches))
+         (layers '((:start 0 :end 4 :props (face italic))
+                   (:start 1 :end 3 :props (face nil help-echo nil))
+                   (:start 6 :end 8 :props (face (:foreground "red")))))
+         (mapped (ebox-surface--patch-property-contributions patches layers 8))
+         (batch (tp-commit-batch-create
+                 :base-revision 1 :target-revision 2 :base-extent 8 :target-extent 8
+                 :patches mapped))
+         (stored (tp-commit-batch-patches batch))
+         (actual (concat (plist-get (nth 0 stored) :replacement)
+                         (plist-get (nth 1 stored) :replacement)
+                         (substring baseline 4 6)
+                         (plist-get (nth 2 stored) :replacement))))
+    (should (equal-including-properties
+             actual (tp--compose-relative-property-contributions baseline layers)))
+    (should (equal-including-properties before patches))
+    (should-not (eq (car patches) (car mapped)))
+    (should-not
+     (ebox-surface--patch-property-contributions
+      patches '((:start 1 :end 7 :props (face italic))) 8))
+    (dolist (invalid '((:start -1 :end 1 :props (face bold))
+                      (:start 0 :end 9 :props (face bold))
+                      (:start 0 :end 1 :props (face))))
+      (should-not
+       (ebox-surface--patch-property-contributions patches (list invalid) 8)))
+    (should
+     (ebox-surface--patch-property-contributions
+      patches '((:start 5 :end 5 :props (face bold))) 8))))
+
+(ert-deftest ebox-child-range-mixed-followup-proof-misses-preserve-fallback ()
+  "Missing ownership or paint coverage returns to exact retained-content work."
+  (dolist (miss '(ownership coverage))
+    (with-temp-buffer
+      (ebox-render-to-buffer
+       (current-buffer) (ebox-child-range-test--snapshot-replacement-root))
+      (ebox-commit
+       (current-buffer)
+       (ebox-child-range-test--replace-snapshot-detail (current-buffer) t))
+      (let* ((function (if (eq miss 'ownership)
+                           'ebox-surface--span-patch-output
+                         'ebox-surface--patch-property-contributions))
+             observed
+             (observer
+              (lambda (original &rest arguments)
+                (setq observed t)
+                (when (eq miss 'ownership)
+                  (prog1 (apply original arguments)
+                    (cl-remf (nth 2 arguments) :span-patch-retained-owned-ranges))))))
+        (advice-add function :around observer)
+        (unwind-protect
+            (ebox-commit
+             (current-buffer)
+             (ebox-child-range-test--mixed-followup-candidate (current-buffer) 2))
+          (advice-remove function observer))
+        (should observed)
+        (ebox-child-range-test--assert-full-render-equivalent (current-buffer))
+        (should-not (plist-get (tp-surface-report ebox-surface--buffer-surface)
+                               :retained-mount-state))))))
+
+(ert-deftest ebox-child-range-mixed-followup-merger-errors-escape-proof-fallback ()
+  "Even a constructor-like merger error propagates once and preserves state."
+  (with-temp-buffer
+    (ebox-render-to-buffer
+     (current-buffer) (ebox-child-range-test--snapshot-replacement-root))
+    (ebox-commit
+     (current-buffer)
+     (ebox-child-range-test--replace-snapshot-detail (current-buffer) t))
+    (let* ((surface ebox-surface--buffer-surface)
+           (state (ebox--buffer-render-state (current-buffer)))
+           (revision (tp-surface-revision surface))
+           (mounts (tp--surface-mounts surface))
+           (index (tp--surface-mount-index surface))
+           (before (buffer-string))
+           (merge-calls 0) (contributed-batches 0) contributed-face
+           (observer
+            (lambda (original &rest arguments)
+              (let* ((patches (mapcar #'copy-sequence (plist-get arguments :patches)))
+                     (patch (cl-find-if
+                             (lambda (entry) (plist-get entry :property-contributions))
+                             patches)))
+                (when patch
+                  ;; Exception-boundary fixture: TP merges only over a present
+                  ;; baseline property.  Keep Ebox's actual generated layers,
+                  ;; adding a baseline only to a detached constructor argument.
+                  ;; Inline row faces would change the fixture's geometry proof.
+                  (let* ((layer (car (plist-get patch :property-contributions)))
+                         (start (plist-get layer :start))
+                         (replacement (copy-sequence (plist-get patch :replacement))))
+                    (should (< start (plist-get layer :end)))
+                    (setq contributed-face (plist-get (plist-get layer :props) 'face))
+                    (should contributed-face)
+                    (put-text-property start (1+ start) 'face '(:slant italic) replacement)
+                    (plist-put patch :replacement replacement)
+                    (setq arguments (plist-put (copy-sequence arguments) :patches patches))
+                    (cl-incf contributed-batches)))
+                (apply original arguments)))))
+      (let ((tp--property-policies (copy-hash-table tp--property-policies))
+            (tp--property-policy-order (copy-sequence tp--property-policy-order)))
+        (tp-define-property-policy
+         (tp-text-property-id 'face)
+         :projector (tp-property-policy-projector
+                     (tp-property-policy (tp-text-property-id 'face)))
+         :merge (lambda (old new)
+                  (should (equal old '(:slant italic)))
+                  (should (equal new contributed-face))
+                  (cl-incf merge-calls)
+                  (signal 'tp-surface-error '(:commit-patch merger-failure))))
+        (advice-add 'tp-commit-batch-create :around observer)
+        (unwind-protect
+            (let ((condition
+                   (should-error
+                    (ebox-commit
+                     (current-buffer)
+                     (ebox-child-range-test--mixed-followup-candidate
+                      (current-buffer) 2))
+                    :type 'tp-surface-error)))
+              (should (equal (seq-take condition 3)
+                             '(tp-surface-error :commit-patch merger-failure))))
+          (advice-remove 'tp-commit-batch-create observer)))
+      (should (= contributed-batches 1))
+      (should (= merge-calls 1))
+      (should (= revision (tp-surface-revision surface)))
+      (should (eq state (tp-surface-client-state surface)))
+      (should (eq state (ebox--buffer-render-state (current-buffer))))
+      (should (eq mounts (tp--surface-mounts surface)))
+      (should (eq index (tp--surface-mount-index surface)))
+      (should (equal-including-properties before (buffer-string)))
+      (ebox-commit
+       (current-buffer)
+       (ebox-child-range-test--mixed-followup-candidate (current-buffer) 2))
+      (ebox-child-range-test--assert-full-render-equivalent (current-buffer))
+      (should (plist-get (tp-surface-report surface) :retained-mount-state)))))
+
+(ert-deftest ebox-child-range-mixed-followup-role-change-keeps-fallback ()
+  "Replacing text with a new box role cannot reuse the old mount topology."
+  (with-temp-buffer
+    (ebox-render-to-buffer
+     (current-buffer) (ebox-child-range-test--snapshot-replacement-root))
+    (ebox-commit
+     (current-buffer)
+     (ebox-child-range-test--replace-snapshot-detail (current-buffer) t))
+    (let ((candidate
+           (ebox-child-range-test--mixed-followup-candidate (current-buffer) 2)))
+      (ebox-candidate-replace-host-ref
+       candidate 'title
+       (ebox-test-box :key 'title :source-identity 'title
+         (ebox-test-text (propertize "title-2" 'face '(:weight bold)))))
+      (ebox-commit (current-buffer) candidate))
+    (ebox-child-range-test--assert-full-render-equivalent (current-buffer))
+    (should-not (plist-get (tp-surface-report ebox-surface--buffer-surface)
+                           :retained-mount-state))))
+
 (ert-deftest ebox-child-range-does-not-reuse-disappeared-key-positionally ()
   "A new keyed item must not inherit a removed peer's runtime identity."
   (let ((buffer (generate-new-buffer " *ebox-range-key-reentry*")))